On the use of stable oxygen isotope (δ¹⁸O) measurements for tracking avian movements in North America

Abstract

Tracking migratory animals has benefitted using measurements of naturally occurring stable isotopes of hydrogen (δ2H) in keratinous tissues such as hair and feathers to link animal origins to continental patterns or isoscapes of δ2H in precipitation. However, for most taxa, much less information exists on the use of stable oxygen isotope ratios (δ18O) despite the fact that δ2H and δ18O are strongly linked in environmental waters through the meteoric relationship and the possibility of using both isotopes to infer greater information on origins and climatic conditions where tissues are grown. A fundamental requirement of using stable isotopes to assign individuals and populations to origins is the development of a rescaling function linking environmental food web signals to the tissue of interest and for birds, this has not been carried out. Here, we derived the relationship between H and O isotopes in known source feathers of 104 individuals representing 11 species of insectivorous passerines sampled across the strong precipitation isoscape of North America. We determined again a strong expected relationship between feather δ2H (δ2Hf) and long-term amount-weighted precipitation δ2H (δ2Hp; r2 = 0.77), but the corresponding relationship between δ18Of and δ18Op was poor (r2 = 0.32) for the same samples. This suggests that δ2H measurements are currently more useful for assignment of insectivorous songbirds to precipitation isoscapes but does not preclude other uses of the δ18Of data. Currently, mechanisms responsible for the decoupling of H and O isotopes in food webs is poorly known, and we advocate a much broader sampling of both isotopes in the same keratinous tissues across precipitation isotope gradients and across taxa to resolve this issue and to increase the power of using water isotopes to track migratory animals.

Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

“…Modeling suggested that these distinctive values could be explained by the expected preferential atomic routing of H from 2 H-enriched marine dietary items to keratin combined with the dominance of 18 O-depleted drinking water on keratin 18 O. This suggests that the dual-isotope system (Hobson et al, 2004;Myers et al, 2012;Hobson and Koehler, 2015). Some potential contributors to the relatively poor relationship in δ 18 O values may be due to the exchanges of O in body water with O in the CO 2 of dissolved body water (McCluney and Sabo, 2010), or that in aquatic organisms, organically bound oxygen, particularly Ehleringer et al, 2008) and Asian cities (n = 25, Thompson et al, 2010) as well as mid-twentieth century indigenous populations (n = 26, Bowen et al, 2009).…”

Endothermic mosasaurs? Possible thermoregulation of Late Cretaceous mosasaurs (Reptilia, Squamata) indicated by stable oxygen isotopes in fossil bioapatite in comparison with coeval marine fish and pelagic seabirds

“…Although the δ 18 O bodywater of modern birds has not been reported extensively, Kerstel et al . () reported that stable oxygen isotopes in the body water of shorebirds occur at ‘natural abundances’ while Hobson & Koehler () suggested a close association between δ 18 O bodywater and meteoric water ingested by migrating terrestrial birds. Schaffner & Swart () reported that ingested water is the only source of δ 18 O bodywater in terrestrial vertebrates including birds, with only minor short term fluctuations due to respiration and metabolism.…”

“…). Although there is no exchange of oxygen with ambient water vapour during respiration in birds (Hobson & Koehler ), Amiot et al . () noted an enrichment of δ 18 O bodywater in semiaquatic crocodiles, which are distantly related to birds (archosaurs) and also use evaporative cooling, of up to 2‰.…”

Natal origin of the invasive biosecurity pest, brown marmorated stink bug (Halyomorpha halys: Penatomidae), determined by dual‐element stable isotope‐ratio mass spectrometry

“…For provenance assignment in ecology, δ 2 H has been the most commonly used isotope marker, largely due to analytical accessibility. δ 18 O has been less commonly used due to analytical difficulties, especially with small samples (discussed below), plus assignment of provenance is potentially complicated due to animals sourcing O from air as well as water and food . However, provenance resolution can be improved by considering δ 2 H and δ 18 O together, as they serve as semi‐independent markers due to differences in evaporative response .…”

“…18 O has been less commonly used due to analytical difficulties, 27 especially with small samples (discussed below), plus assignment of provenance is potentially complicated due to animals sourcing O from air as well as water and food. 28 However, provenance resolution can be improved by considering 2 H and 18 O together, as they serve as semi-independent markers due to differences in evaporative response. 27,29,30 Additionally and importantly, data derived from separate isotope systems also permits the use of more powerful, multivariate statistical analyses.…”